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launch gazebo and spawn our simple_joint robot - apply torque to link from gazebo gui - Add gazebo_force plugin - apply torque from command line

launch gazebo#

urdf#

```xml title=”robot_v1.urdf|

<material name="blue">
    <color rgba="0 0 0.8 1"/>
</material>

<material name="black">
    <color rgba="0 0 0 1"/>
</material>

<joint name="word2base" type="fixed">
    <parent link="world"/>
    <child link="base_link"/>
    <origin xyz="0.0 0.0 0.12" rpy="0.0 0.0 0.0"/>
</joint>
<link name="base_link">
    <inertial>
        <mass value="10" />
        <inertia ixx="0.4" ixy="0.0" ixz="0.0" iyy="0.4" iyz="0.0" izz="0.2"/>
    </inertial>
    <collision>
        <geometry>
            <cylinder radius="0.05" length="0.24" />
        </geometry>
    </collision>
    <visual>
        <geometry>
            <cylinder radius="0.05" length="0.24" />
        </geometry>
        <material name="black"/>
    </visual>
</link>

<link name="second_link">
    <inertial>
        <mass value="0.18" />
        <inertia ixx="0.0002835" ixy="0.0" ixz="0.0" iyy="0.0002835" iyz="0.0" izz="0.000324" />
    </inertial>
    <origin rpy="0.0 0.0 0.0" xyz="0.0 0.0 0.0" />
    <collision>
        <geometry>
            <box size="0.05 0.05 0.15" />
        </geometry>
    </collision>
    <visual>
        <geometry>
            <box size="0.05 0.05 0.15" />
        </geometry>
        <material name="blue"/>
    </visual>
</link>

<joint name="base_to_second_joint" type="continuous">
    <parent link="base_link"/>
    <child link="second_link"/>
    <axis xyz="0 0 1"/>
    <origin xyz="0.0 0.0 0.2" rpy="0.0 0.0 0.0"/>
</joint>

<gazebo>
    <plugin name="gazebo_ros_joint_state_publisher" filename="libgazebo_ros_joint_state_publisher.so">
        <update_rate>50</update_rate>
        <joint_name>base_to_second_joint</joint_name>
    </plugin>
</gazebo>

<gazebo reference="base_link">
    <material>Gazebo/Black</material>
</gazebo>
<gazebo reference="second_link">
    <material>Gazebo/Red</material>
</gazebo>

```

launch#

python title="gz_sim.launch.py" from launch import LaunchDescription import os from launch_ros.actions import Node from ament_index_python.packages import get_package_share_directory from launch.actions import AppendEnvironmentVariable, DeclareLaunchArgument from launch.substitutions import LaunchConfiguration from launch.actions import IncludeLaunchDescription from launch.launch_description_sources import PythonLaunchDescriptionSource import xacro PACKAGE = "simple_joint" WORLD = "empty.world" URDF = "robot_v1.urdf" def generate_launch_description(): ld = LaunchDescription() pkg = get_package_share_directory(PACKAGE) gazebo_pkg = get_package_share_directory('gazebo_ros') verbose = LaunchConfiguration("verbose") arg_gazebo_verbose = DeclareLaunchArgument("verbose", default_value="true") world = LaunchConfiguration("world") arg_gazebo_world = DeclareLaunchArgument("world", default_value=WORLD) resources = [os.path.join(pkg, "worlds")] resource_env = AppendEnvironmentVariable( name="GAZEBO_RESOURCE_PATH", value=":".join(resources) ) sim_time = LaunchConfiguration("sim_time") arg_sim_time = DeclareLaunchArgument("sim_time", default_value="true") robot_description_path = os.path.join(pkg, "urdf", URDF) doc = xacro.parse(open(robot_description_path)) xacro.process_doc(doc) robot_description = doc.toxml() robot_state_publisher = Node( package="robot_state_publisher", executable="robot_state_publisher", parameters=[{"use_sim_time": sim_time, "robot_description": robot_description}], ) gazebo = IncludeLaunchDescription( PythonLaunchDescriptionSource([os.path.join( gazebo_pkg, 'launch', 'gazebo.launch.py')]), launch_arguments={'verbose': verbose, "world": world}.items() ) spawn_entity = Node( package="gazebo_ros", executable="spawn_entity.py", arguments=["-entity", "demo", "-topic", "robot_description", "-z", "0.0"], output="screen", ) ld.add_action(resource_env) ld.add_action(arg_gazebo_verbose) ld.add_action(arg_gazebo_world) ld.add_action(arg_sim_time) ld.add_action(robot_state_publisher) ld.add_action(gazebo) ld.add_action(spawn_entity) return ld


Apply torque#

  • Apply torque to joint

gazebo joint state plugin

<gazebo>
    <plugin name="gazebo_ros_joint_state_publisher" filename="libgazebo_ros_joint_state_publisher.so">
        <update_rate>50</update_rate>
        <joint_name>base_to_second_joint</joint_name>
    </plugin>
</gazebo>


Apply Force/ Torque using Wrench msg#

Create topic with Wrench message

Note

xml <joint name="base_to_second_joint" type="continuous"> <parent link="base_link"/> <child link="second_link"/> <axis xyz="0 0 1"/> <origin xyz="0.0 0.0 0.2" rpy="0.0 0.0 0.0"/> <dynamics damping="0.1" friction="1"/> </joint>

xml <gazebo> <plugin name="gazebo_ros_force" filename="libgazebo_ros_force.so"> <link_name>second_link</link_name> <force_frame>world</force_frame> </plugin> </gazebo>

### Wrench msg
ros2 topic pub --once /gazebo_ros_force geometry_msgs/msg/Wrench "{force: {x: 0.0, y: 0.0, z: 0.0}, torque: {x: 0.0,y: 0.0,z: 1.1}}"


Reference#